5 ms·

The Orphan Tsunami of 1700 [pdf]

33 points by oliverkwebb 11mo ago

ogogmad 11mo ago
Just learnt something from the article: It's interesting that the warping of the seafloor is what causes tsunamis, and not the shaking itself. It explains why a shoreline might sometimes recede away before a tsunami's crest strikes: The recession is caused by the seawater dropping with the seafloor, while the forward surge is caused by the ensuing bounce.
- MontagFTB 11mo ago
  The largest tsunami on record came from a landslide in a bay: https://en.wikipedia.org/wiki/1958_Lituya_Bay_earthquake_and_megatsunami https://en.wikipedia.org/wiki/1958_Lituya_Bay_earthquake_and...
  - buildbot 11mo ago
    Yeah that'll happen when a good chunk of a mountain basically drops into your body of water, lol: "The large mass of rock, acting as a monolith (thus resembling high-angle asteroid impact), struck with great force the sediments at bottom of Gilbert Inlet at the head of the bay. The impact created a large crater and displaced and folded recent and Tertiary deposits and sedimentary layers to an unknown depth." With updated modeling showing that impact triggering the glacier to lift and subsequently release even more material, it's shocking anyone in the bay survived at all. Edit - found a video with said papers modeling implemented, pretty neat: https://www.youtube.com/watch?v=B1axr5YGRwQ https://www.youtube.com/watch?v=B1axr5YGRwQ
    - southernplaces7 11mo ago
      Much of the literature references this as the biggest ever tsunami at 500+ meters, but an account from one of the survivors who was there on his fishing boat (with his 7-year-old son!) said this specific thing: "The wave definitely started in Gilbert Inlet, just before the end of the quake. It was not a wave at first. It was like an explosion, or a glacier sluff. The wave came out of the lower part, and looked like the smallest part of the whole thing. The wave did not go up 1,800 feet, the water splashed there." Still insane, but it was the immediate splash that scoured away trees and soil cover up to 527 meters up the mountain face, not a proper tsunami. Both the fisherman and his son survived btw.
      - buildbot 11mo ago
        Yeah I personally agree it’s not quite the same as if the pacific ocean was coming up 527 meters before hitting the shore :)
        southernplaces7 11mo ago
        I'd absolutely love to see something like this live, in the flesh, obviously from far enough to survive it. It would be one of those spectacles for completely flabbergasting one's sense of importance in a self-remaking world.
- pixl97 11mo ago
  Dropping or rising. At the borders of the sea and land plates the sea plates are slipping slowly below the continental crust. Pieces of the land crust get caught and dragged down. Over long periods of time you'll see forested land get dragged down below sea level and flooded to die. The a rupture will occur, and in the biggest earthquakes you can get a fault that can rise 20 meters almost instantly causing trillions of tons of ocean to suddenly have to go somewhere. After the quake and tsunami you'll see the flooded forests can be many meters above land were new forest will grow and slowly start sinking again.
jmward01 11mo ago
Cascadia has become a little bit of an obsession for me. I had my house retrofitted to help it withstand the inevitable next really big one that is coming because of what I have learned about it (I am also well above the tsunami flood zone). Subduction zones are crazy powerful but it looks like we are finally starting to learn important things about them. The challenge though is getting people to accept that they are real and will happen and entire cities need to move because of them (I'm looking at you Ocean Shores). Side note, any actual geologists in the room? The recent Philippians 7.6 looks like it may be following a growing pattern of megathrust forshocks to my -deeply- untrained eye. Does someone with actual knowledge and training have a take on that?
- VoidWarranty 11mo ago
  Got any recs for contractors in the area to do the work? What should I get done? (ranch 2 story built in 90s). Cost to expect? Been having bad luck lately with bids and sketch contractors. Takes a lot of effort to sift through.
  - jmward01 11mo ago
    This was close to DYI with me and the local handyman figuring out a good way to tie my house to its foundation. Not a full retrofit but pretty good for my 100yo house with nothing remotely close to modern design. Here are some resources I found useful though. https://dnr.wa.gov/sites/default/files/2025-03/ger_homeowners_guide_earthquakes.pdf https://dnr.wa.gov/sites/default/files/2025-03/ger_homeowner... https://www.wabo.org/earthquake-home-retrofit https://www.wabo.org/earthquake-home-retrofit
    - VoidWarranty 11mo ago
      Thanks! I'll check this out!
- ogogmad 11mo ago
  Sea wall?
458QxfC2z3 11mo ago
Long article from 2015 in The New Yorker about the Cascadia subduction zone: https://www.newyorker.com/magazine/2015/07/20/the-really-big-one https://www.newyorker.com/magazine/2015/07/20/the-really-big...

33 points by oliverkwebb 11mo ago

Just learnt something from the article: It's interesting that the warping of the seafloor is what causes tsunamis, and not the shaking itself. It explains why a shoreline might sometimes recede away before a tsunami's crest strikes: The recession is caused by the seawater dropping with the seafloor, while the forward surge is caused by the ensuing bounce.

MontagFTB 11mo ago
The largest tsunami on record came from a landslide in a bay: https://en.wikipedia.org/wiki/1958_Lituya_Bay_earthquake_and_megatsunami https://en.wikipedia.org/wiki/1958_Lituya_Bay_earthquake_and...
- buildbot 11mo ago
  Yeah that'll happen when a good chunk of a mountain basically drops into your body of water, lol: "The large mass of rock, acting as a monolith (thus resembling high-angle asteroid impact), struck with great force the sediments at bottom of Gilbert Inlet at the head of the bay. The impact created a large crater and displaced and folded recent and Tertiary deposits and sedimentary layers to an unknown depth." With updated modeling showing that impact triggering the glacier to lift and subsequently release even more material, it's shocking anyone in the bay survived at all. Edit - found a video with said papers modeling implemented, pretty neat: https://www.youtube.com/watch?v=B1axr5YGRwQ https://www.youtube.com/watch?v=B1axr5YGRwQ
  - southernplaces7 11mo ago
    Much of the literature references this as the biggest ever tsunami at 500+ meters, but an account from one of the survivors who was there on his fishing boat (with his 7-year-old son!) said this specific thing: "The wave definitely started in Gilbert Inlet, just before the end of the quake. It was not a wave at first. It was like an explosion, or a glacier sluff. The wave came out of the lower part, and looked like the smallest part of the whole thing. The wave did not go up 1,800 feet, the water splashed there." Still insane, but it was the immediate splash that scoured away trees and soil cover up to 527 meters up the mountain face, not a proper tsunami. Both the fisherman and his son survived btw.
    - buildbot 11mo ago
      Yeah I personally agree it’s not quite the same as if the pacific ocean was coming up 527 meters before hitting the shore :)
      - southernplaces7 11mo ago
        I'd absolutely love to see something like this live, in the flesh, obviously from far enough to survive it. It would be one of those spectacles for completely flabbergasting one's sense of importance in a self-remaking world.
pixl97 11mo ago
Dropping or rising. At the borders of the sea and land plates the sea plates are slipping slowly below the continental crust. Pieces of the land crust get caught and dragged down. Over long periods of time you'll see forested land get dragged down below sea level and flooded to die. The a rupture will occur, and in the biggest earthquakes you can get a fault that can rise 20 meters almost instantly causing trillions of tons of ocean to suddenly have to go somewhere. After the quake and tsunami you'll see the flooded forests can be many meters above land were new forest will grow and slowly start sinking again.

jmward01 11mo ago

Cascadia has become a little bit of an obsession for me. I had my house retrofitted to help it withstand the inevitable next really big one that is coming because of what I have learned about it (I am also well above the tsunami flood zone). Subduction zones are crazy powerful but it looks like we are finally starting to learn important things about them. The challenge though is getting people to accept that they are real and will happen and entire cities need to move because of them (I'm looking at you Ocean Shores). Side note, any actual geologists in the room? The recent Philippians 7.6 looks like it may be following a growing pattern of megathrust forshocks to my -deeply- untrained eye. Does someone with actual knowledge and training have a take on that?

VoidWarranty 11mo ago
Got any recs for contractors in the area to do the work? What should I get done? (ranch 2 story built in 90s). Cost to expect? Been having bad luck lately with bids and sketch contractors. Takes a lot of effort to sift through.
- jmward01 11mo ago
  This was close to DYI with me and the local handyman figuring out a good way to tie my house to its foundation. Not a full retrofit but pretty good for my 100yo house with nothing remotely close to modern design. Here are some resources I found useful though. https://dnr.wa.gov/sites/default/files/2025-03/ger_homeowners_guide_earthquakes.pdf https://dnr.wa.gov/sites/default/files/2025-03/ger_homeowner... https://www.wabo.org/earthquake-home-retrofit https://www.wabo.org/earthquake-home-retrofit
  - VoidWarranty 11mo ago
    Thanks! I'll check this out!
ogogmad 11mo ago
Sea wall?

458QxfC2z3 11mo ago

Long article from 2015 in The New Yorker about the Cascadia subduction zone: https://www.newyorker.com/magazine/2015/07/20/the-really-big-one https://www.newyorker.com/magazine/2015/07/20/the-really-big...